A printed circuit board (PCB) is means that fixes and electrically connects various electronic components to construct a circuit. Generally, the printed circuit board includes an insulating base, a conductive pattern on the insulating base, and a plurality of through-holes through which components are fixed and electrically connected to each other.
Printed circuit boards can be classified into rigid printed circuit boards (rigid PCBs), flexible printed circuit boards (FPCBs), and rigid-flexible printed circuit boards (R-F PCBs). In the rigid PCBs, a copper foil is attached to a core material obtained by reinforcing an epoxy resin with a suitable material such as a glass fiber. In the flexible PCBs, a copper foil is attached to polyimide. The R-F PCBs are combinations of rigid PCBs and flexible PCBs to possess the advantages of the two PCBs. The application of these printed circuit boards is determined depending on their characteristics. With the recent trend toward lightweight, slim and small-sized electronic devices, there has been an increasing demand for printed circuit boards taking up a little space. Miniaturization of printed circuit boards requires lamination of circuit patterns or a reduction in spacing between the interconnections of circuits.
According to a traditional method for forming a circuit pattern in a printed circuit board, a dry film is used to form a masking pattern on a copper foil, and the copper foil is etched to form a circuit. This method has a limitation in controlling the spacing between the circuit interconnections to 60 micrometers or less. In attempts to overcome the limitation encountered with the formation of fine circuit patterns, new techniques, for example, a semi-additive process (SAP), have recently been introduced. The semi-additive process is a concept opposite to traditional etching processes. According to the semi-additive process, an area other than an area for circuit formation is masked with a suitable masking material such as a dry film, followed by direct plating on the area for circuit formation to form a conductive pattern.
Even when the semi-additive process is applied, the use of a thin copper foil is required for the formation of a fine pattern. The copper foil is a base layer serving as an electrode for direct plating. However, thin copper foils are available from only a few suppliers because they are difficult to produce. Due to high price of thin copper foils, PCB manufacturers purchase cheap thick copper foils and etch them to desired thicknesses before use. However, the additional etching involves an additional increase in production cost and causes environmental pollution problems.
Many production processes of copper foils for printed circuit boards are widely known. For example, Korean Patent Publication No. 2012-0084441 discloses a copper foil for the production of a copper clad laminate and a copper clad laminate including the copper foil. However, when a copper foil is laminated on a carrier, diffusion occurs between the carrier aluminum and the copper. This diffusion makes it difficult to peel off the aluminum carrier layer, and as a result, a uniform surface of the copper foil is difficult to obtain. Further, Korean Patent Registration No. 728764 introduces a technique associated with the deposition of copper particles by sputtering. This technique contributes to simplification of the production procedure, improvement of production efficiency, and slimness of a substrate. This patent publication, however, does not disclose the production of a thin copper foil.